The system shown in FIG. 1 is an example of the above-mentioned type of audio equipment. In this prior art equipment, the parts which an operator needs for operation of the system i.e., the operator controls such as knobs and buttons, the display section for displaying operational states, and the drive deck (the mechanical components), are provided in a console unit or in the dashboard, and the other parts are provided in hidden-away locations as much as possible. This arrangement provides the freedom of combining each of the units with other units and it is contemplated that various different types of components, e.g., personal radio communication devices, compact disk units and so, can be combined to expand the system as desired.
In FIG. 1, the components shown in double-line enclosures are provided in the console or dashboard unit, which comprises operator control section 16, display section 17, and a deck section 18. The parts shown in single-line enclosures are provided in hideaway locations. The latter include a tuner unit 19, a preamplifier unit 23, a unit 24 for singing an air to the tune of a melody recorded on a recording medium such as magnetic tape (hereinafter referred to as "the karaoke unit" or "the karaoke apparatus"), a graphic equalizer unit 25, an ASL unit 26 (an apparatus to control the volume automatically), and a power amplifier unit 27. These components comprise the audio signal processing portion of the system.
The units are connected to one another by a connecting cable 20. The cable 20 is composed of a microcomputer bus line 21 and a two-core shielding connection line 22 which comprises an L & R channel line and a grand line. Microcomputer 1 and a plurality of microcomputers 2 are respectively connected via the microcomputer bus line 21, wherein the microcomputer 1 works as a master source and each microcomputer 2 works as a terminal satisfying its unit specification.
Each of the microcomputers 1 and 2 are connected with the circuits 4 to 11 within the units 16-26. When the circuits 4, 5 of the operator control section and the display section do not have any signal sources, then they would not be connected with the audio bus line 22.
A microphone 12 for the karaoke apparatus is connected with the circuits 9 of the karaoke unit 24. A microphone 13 for detecting the pink noise is connected with the circuit 10 of the graphic equalizer 25. Further, a microphone 14 for detecting the running noise is connected with the circuit 11 of the ASL unit 26. In addition, speakers 15 for the L & R channel are connected with the power amplifier units 27.
When the operator manipulates the operator controls in this prior art audio equipment, each unit is controlled by the microcomputer 1 and a result of the control state is displayed on the display 17.
Suppose that the deck section 18 starts in operation. The audio signal from the circuit 6 is fed to the audio source bus line 22 shown by the dotted line in FIG. 1 and is fed to the circuit 8 of the preamplifier unit 23, wherein signal processing to effect volume control and tone control is performed. The processed signal is fed to the audio signal line 28, which is connected with the power source. Therefore, conventional audio processing is done toward said signal so that finally the speaker 15 is driven through the power amplifier 27.
In the case of the karaoke operation, the audio signal is detected through the microphone 12 connected with the circuit 9 of the karaoke unit 24. This detected signal is subjected to echo processing and mixing and fed to the audio signal line 28. The microphone 13 connected with the graphic equalizer 25 is used for controlling the automatic frequency characteristic and detects the pink noise transmitted inside the car. That is to say, the pink noise originated at the circuit 10 is amplified through the power amplifier and put on the air over the speaker 15 in the car. Owing to the fact that the microphone 13 then detects the sounded pink noise, the circuit 10 discriminates the level at each frequency processed by the graphic equalizer and controls the equalizer so as to produce a flat frequency characteristic. Since the microphone 14 of the ASL unit 26 detects the running noise inside the car, the circuit 11 controls the volume and the tone, etc., on the base of the noise for compensating the Masking Phenomenon which is brought by the running noise.
FIG. 2 shows the block diagram of the audio signal system of the prior art. The audio outputs of the sources, i.e., the deck section, the tuner unit and other source units, are connected to the audio source bus line as the current source through a voltage-current conversion circuit 29. The signal currents from the plural sources are fed to a current-voltage conversion circuit 30 of the preamplifier 23 to convert the currents into voltage, which are fed to another audio unit through the volume tone circuit 31.
Since the car-mounted audio equipment of the prior art is configured as mentioned above, separate microphones have to be provided for the karaoke unit 24, the graphic equalizer unit 25, and the ASL unit 26.